Suspicions swirled around the Duke and Duchess of Windsor, for example. So much so that the Duke was conveniently appointed as Governor of the Bahamas where he sat out the war in hot and humid "exile".
One would hope that Charles will be careful of indulging his exotic tastes for certain foreign ideologies more carefully than did the Duke. It may turn up to bite him in his royal posterior some day.
Leni
Nazi sympathy was pretty common in the US at that time too - Henry Ford was funding the Nazi party for 16 years before he received his Grand Cross of the German Eagle medal from Hitler in 1938. At the outbreak of war in 1939, Ford-Werke in Germany placed itself at the disposal of the wehrmacht to produce armaments to be used against Britain - allegedly an ally of the US!
Then of course there was Dubya's grandad Prescott, whose Nazi sympathies are well-documented right through to the current son-of-a-nazi dictator (sorry, governor!) of California.
Despite the nazi sympathies of some in Britain, we declared war the same day one of our allies was attacked by the Nazis. It took another two years and an attack by the japs before the US joined the war, so perhaps those nazi sympathies were a lot stronger in the US than in Britain?